The present invention is related to autotransformers, and in particular to a dual-input nine-phase autotransformer.
An autotransformer is an electrical transformer with only one winding that acts as both the primary and secondary winding associated with a typical transformer. As a result, autotransformers can be smaller, lighter and cheaper than standard dual-winding transformers. This makes autotransformers an attractive alternative in application (such as aircraft applications) in which weight is an important factor.
Autotransformers are often-times employed in AC-DC power conversion systems. In theory, AC-DC power conversion may be accomplished with a plurality of diode pairs, each pair connected to a different phase of the AC input, to provide a rectified output. However, this type of rectifier leads to substantial current harmonics that pollute the electric power generation and distribution system. To reduce current harmonics, autotransformers are employed to increase the number of AC phases supplied to the rectifier unit. For example, in an eighteen-pulse converter (an AC-DC converter having an eighteen step staircase current waveform at each of the AC inputs) the autotransformer is used to transform the three-phase AC input, whose phases are spaced at 120°, into a system with nine phases spaced at 40°. This has the effect of reducing the harmonics associated with the AC-DC conversion.